DEPOSITIONAL FEATURES AND CONTROLING FACTORS OF PLIOCENE-MIOCENE DEPOSITS IN ALBERT GRABEN,UGANDA

The Albert Graben,Uganda,located in the northern part of the west branch of The East African Rift Valley,is an intra-continental rift basin developed in Late Miocene. The basin is rich in oil and gas,and the Miocene-Pliocene sandstone is the main reservoir. Based on well logs,cores and palynology data,the authors conclude that the climate was warm and humid there in Miocene to Pliocene,and the lake level rose with oscillation. The source system of the graben is complex,The Victoria Nile,Albert Nile and Kafu Rivers are the main streams. The graben,from north to south,might be divided into northern gentle slope belt,middle fault step belt,southern steep fault belt,southern fault step belt and steep slope belt. The northern gentle slope belt is filled with fluvial-deltaic system distributed along the graben axis. The middle fault step belt,southern Steep fault belt and southern fault step belt are featured by several fan delta systems distributed perpendicular to the long axis of the graben,while the southern steep slope belt is deposited with fan delta and sub-lacustrine fan deposits distributed along the graben axis. The sedimentation of the graben is controlled by source systems,tectonic belts,lake level fluctuation and climate changes. Based on above research,it is concluded that the northern part of the graben,the eastern boundary fault downthrow area and the southern part of the graben,which have good reservoir and seal assemblage,are the most favorable area for exploration.